Photoisomerizable mesogenic molecules which change their shape on photo-irradiation ae known in prior art. When irradiated e.g. with UV light, they show E-Z or cis-trans isomerization.
Photoisomerizable compounds that are mesogenic, i.e. exhibit or induce liquid crystal phase behavior, can be used inter alia to prepare a patterned liquid crystal polymer film, e.g., according to the following method. A polymerizable nematic liquid crystal mixture containing a photoisomerizable polymerizable mesogenic compound is coated as a thin film onto a substrate and aligned into uniform orientation. Selected regions of the coated film are then subjected to photoirradiation, e.g., through a photomask. This causes isomerization of the photoisomerizable compound, leading to a change of the alignment in the irradiated regions, e.g., from nematic orientation to a distorted orientation or to an isotropic unoriented state, and thus to a pattern in the film. The pattern is then frozen in by in-situ polymerization of the coated film, e.g., by thermal or photopolymerization.
The patterned films can be used as optical element like colour filters or polarization beam splitters, as information storage device, anisotropic membranes for the permeation of, e.g., gases, or in nonlinear optics.
Gangadhara and Kishore in Macromolecules, 1995, 28, 806-815, the entire disclosure of which is incorporated into this application by way of reference, have reported that polymerizable mesogenic compounds comprising a bis(benzylidene)-cyclohexanone unit undergo EZ photoisomerisation and change from the EE conformation to the isomeric EZ, or ZZ forms as shown below. 
The EZ photoisomerisation is reported to disrupt the parallel stacking of the mesogens, resulting in the transition from the liquid crystal phase to the isotropic phase.
However, the article of Gangadhara and Kishore only discloses compounds having mono-polymerizable groups and mono-mesogenic groups attached the central cyclohexanone core. Furthermore, the compounds disclosed in this article only have narrow liquid crystal phase ranges with low clearing points, or do not show a liquid crystal phase at all.
Therefore, there is a demand for photoisomerizable compounds which are easy to synthesize in a large range of derivatives, show broad liquid crystalline phases with high clearing points and, when added to a liquid crystalline host mixture, do not affect the properties of the host mixture.
The invention has the aim of providing novel compounds having the above properties, but not having the disadvantages of the compounds of discussed above. Another aim of the invention is to extend the pool of photoisomerizable compounds available in the art.
It has been found that the above aims can be achieved by providing cycloalkanone derivatives as described herein.
Definition of Terms
The terms ‘liquid crystalline or mesogenic material’ or ‘liquid crystalline or mesogenic compound’ denotes materials or compounds comprising one or more rod-shaped, lath-shaped or disk-shaped mesogenic groups, i.e., groups with the ability to induce liquid crystal phase behavior. Rod-shaped and lath-shaped mesogenic groups are especially preferred. The compounds or materials comprising mesogenic groups do not necessarily have to exhibit a liquid crystal phase themselves. It is also possible that they show liquid crystal phase behavior only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerized.
The term ‘reactive mesogen’ means a polymerizable mesogenic compound.
For the sake of simplicity, the term ‘liquid crystal material’ is used hereinafter for both liquid crystal materials and mesogenic materials.
The term ‘film’ includes self-supporting, i.e., free-standing, films that show more or less pronounced mechanical stability and flexibility, as well as coatings or layers on a supporting substrate or between two substrates.
The term ‘photoisomerizable group’ means a group that shows isomerization, for example, cis-trans or E-Z isomerization, imparting a change in shape upon photoirradiation with a suitable wavelength, preferably in the range from 250 to 400 nm, very preferably from 300 to 400 nm.